# NTP Server The NTP (Network Time Protocol) server provides accurate time synchronization for network clients. It supports both standalone operation with a local reference clock and hybrid mode where it synchronizes with upstream servers while serving time to downstream clients. > [!NOTE] > The NTP server is mutually exclusive with the NTP client in system > configuration context. ## Standalone Mode Configure a standalone NTP server using only a local reference clock: 
admin@example:/> configure
admin@example:/config/> edit ntp
admin@example:/config/ntp/> leave
When setting up NTP via the CLI the system automatically configures a local reference clock. The default [stratum](#ntp-stratum-levels) is 16 (unsynchronized), which is suitable for isolated networks. For production use, configure a specific stratum level: 
admin@example:/config/> edit ntp
admin@example:/config/ntp/> set refclock-master master-stratum 10
admin@example:/config/ntp/> leave
## GPS Reference Clock A GPS/GNSS receiver can be used as an NTP reference clock source, providing stratum 1 time derived from the GPS satellite constellation. This requires a GPS hardware component to be configured first, see [Hardware — GPS/GNSS Receivers](hardware.md#gpsgnss-receivers). ### Basic setup Add a GPS receiver as a reference clock source: 
admin@example:/config/> edit ntp
admin@example:/config/ntp/> edit refclock-master source gps0
admin@example:/config/ntp/refclock-master/source/gps0/> set poll 2
admin@example:/config/ntp/refclock-master/source/gps0/> set precision 0.1
admin@example:/config/ntp/refclock-master/source/gps0/> end
admin@example:/config/ntp/> leave
Tunable parameters: | Parameter | Default | Description | |-------------|--------:|----------------------------------------------------| | `poll` | `2` | Polling interval in log2 seconds (2 = 4s) | | `precision` | `0.1` | Assumed precision in seconds (0.1 = 100ms) | | `refid` | `"GPS"`| Reference identifier (e.g., `GPS`, `GNSS`, `GLO`) | | `prefer` | `false` | Prefer this source over other reference clocks | | `pps` | `false` | Enable PPS for microsecond-level accuracy | | `offset` | `0.0` | Constant offset correction in seconds | | `delay` | `0.0` | Assumed maximum delay from the receiver | ### PPS (Pulse Per Second) When the GPS receiver provides a PPS signal, enable the `pps` option for microsecond-level accuracy. With PPS, the GPS time provides the initial lock and the PPS edges discipline the clock: 
admin@example:/config/ntp/> edit refclock-master source gps0
admin@example:/config/ntp/refclock-master/source/gps0/> set pps true
admin@example:/config/ntp/refclock-master/source/gps0/> set precision 0.000001
admin@example:/config/ntp/refclock-master/source/gps0/> end
admin@example:/config/ntp/> leave
### Monitoring The `show ntp` command shows the GPS receiver as the reference clock source: 
admin@example:/> show ntp
Mode                : Server (GPS reference clock: gps0)
Port                : 123
Stratum             : 1
Ref time (UTC)      : Sun Feb 08 19:44:36 2026
Use `show ntp source` to see GPS reference clock details: 
admin@example:/> show ntp source
Reference Clock     : gps0 (u-blox)
Status              : selected
Fix Mode            : 3D
Satellites          : 9/17 (used/visible)
## Server Mode Synchronize from upstream NTP servers while serving time to clients: 
admin@example:/config/> edit ntp
admin@example:/config/ntp/> edit unicast-configuration 0.pool.ntp.org type uc-server
admin@example:/config/ntp/…/0.pool.ntp.org/type/uc-server/> set iburst true
admin@example:/config/ntp/…/0.pool.ntp.org/type/uc-server/> end
admin@example:/config/ntp/> edit unicast-configuration 1.pool.ntp.org type uc-server
admin@example:/config/ntp/…/1.pool.ntp.org/type/uc-server/> set iburst true
admin@example:/config/ntp/…/1.pool.ntp.org/type/uc-server/> end
admin@example:/config/ntp/> leave
The `unicast-configuration` uses a composite key with both address and type. Both hostnames and IP addresses are supported. The `iburst` option enables fast initial synchronization. ## Peer Mode In peer mode, two NTP servers synchronize with each other bidirectionally. Each server acts as both client and server to the other: **First peer:** 
admin@peer1:/config/> edit ntp
admin@peer1:/config/ntp/> edit unicast-configuration 192.168.1.2 type uc-peer
admin@peer1:/config/ntp/…/192.168.1.2/type/uc-peer/> end
admin@peer1:/config/ntp/> set refclock-master master-stratum 8
admin@peer1:/config/ntp/> leave
**Second peer:** 
admin@peer2:/config/> edit ntp
admin@peer2:/config/ntp/> edit unicast-configuration 192.168.1.1 type uc-peer
admin@peer2:/config/ntp/…/192.168.1.1/type/uc-peer/> end
admin@peer2:/config/ntp/> set refclock-master master-stratum 8
admin@peer2:/config/ntp/> leave
This configuration provides mutual synchronization between peers. If one peer fails, the other continues to serve time to clients. > [!NOTE] > The `iburst` and `burst` options are not supported in peer mode. ### Peer Selection in Symmetric Mode When both peers have the same stratum (as in the example above where both are stratum 8), NTP's clock selection algorithm uses the **Reference ID** as the tie-breaker. The Reference ID is typically derived from the peer's IP address when using a local reference clock. This means the peer with the **numerically lower IP address** will be selected as the sync source by the other peer. In the example above: - peer1 (192.168.1.1) has a lower Reference ID - peer2 (192.168.1.2) will select peer1 as sync source This behavior is deterministic and ensures stable clock selection. If you need a specific peer to be selected, configure it with a lower stratum level than the other peer. ## Timing Configuration ### Poll Intervals Control how often the NTP server polls upstream sources: 
admin@example:/config/ntp/> edit unicast-configuration 0.pool.ntp.org type uc-server
admin@example:/config/ntp/…/0.pool.ntp.org/type/uc-server/> set minpoll 4
admin@example:/config/ntp/…/0.pool.ntp.org/type/uc-server/> set maxpoll 10
admin@example:/config/ntp/…/0.pool.ntp.org/type/uc-server/> end
Poll intervals are specified as powers of 2: - `minpoll 4` = poll every 2^4 = 16 seconds (minimum polling rate) - `maxpoll 10` = poll every 2^10 = 1024 seconds (maximum polling rate) - Defaults: minpoll 6 (64 seconds), maxpoll 10 (1024 seconds) Use shorter intervals (minpoll 2-4) for faster convergence in test environments or peer configurations. Use defaults for production servers. ### Fast Initial Synchronization The `makestep` directive is automatically configured with safe defaults (1.0 seconds threshold, 3 updates limit) when creating an NTP server. This is critical for embedded systems without RTC that boot with epoch time. To customize the values: 
admin@example:/config/ntp/> edit makestep
admin@example:/config/ntp/makestep/> set threshold 2.0
admin@example:/config/ntp/makestep/> set limit 1
admin@example:/config/ntp/makestep/> end
- **threshold** - If clock offset exceeds this (in seconds), step immediately instead of slewing slowly - **limit** - Number of updates during which stepping is allowed. After this, only gradual slewing is used for security With these defaults, a device booting at epoch time (1970-01-01) will sync to correct time within seconds instead of hours. ## Monitoring For a quick overview: To view the sources being used by the NTP client, run: 
admin@example:/> show ntp
Mode                : Client
Stratum             : 3
Ref time (UTC)      : Sat Jan 24 23:41:42 2026

ADDRESS         MODE    STATE     STRATUM  POLL
147.78.228.41   server  outlier         2   64s
192.168.0.1     server  unusable        0  128s
176.126.86.247  server  selected        2   64s
Check NTP source status: 
admin@example:/> show ntp source
MS  Name/IP address  Stratum  Poll  Reach  LastRx          Last sample
^+  147.78.228.41          2     6    007      15  -431us +/- 33.573ms
^*  176.126.86.247         2     6    007      14   -389us +/- 4.307ms
For detailed information about a specific source: 
admin@example:/> show ntp source 176.126.86.247
Address             : 176.126.86.247
Mode                : Server (client mode) [^]
State               : Selected sync source [*]
Configured          : Yes
Stratum             : 2
Poll interval       : 7 (2^7 seconds = 128s)
Reachability        : 377 (octal) = 11111111b
Last RX             : 75s ago
Offset              : +2.0us (+0.002000ms)
Delay               : 4.270ms (0.004270s)
Dispersion          : 205.0us (0.205000ms)
## NTP Stratum Levels NTP uses a hierarchical system called **stratum** to indicate distance from authoritative time sources: - **Stratum 0**: Reference clocks (atomic clocks) - **Stratum 1**: Servers directly connected to stratum 0 (e.g., GPS receivers) - **Stratum 2-15**: Servers that sync from lower stratum (each hop adds one) - **Stratum 16**: Unsynchronized (invalid) The default stratum (16) is not suitable for distributing time in isolated networks, so when setting up an NTP server remember to adjust this value. Use, e.g., `10`, this is a safe, low-priority value that ensures clients will prefer upstream-synchronized servers (stratum 1-9) while still having a fallback time source in isolated networks.